Wavefront sensing is an optical technique for measuring a wavefront of a light beam. A wavefront refers to the locus of points in which a propagating optical wave has the same phase.
Wavefront sensing is widely used in astronomical telescopes and laser communication systems to measure effects of atmospheric distortion. Wavefront sensing is also used in optical fabrication and in retinal imaging systems to quantify optical aberrations. Further, wavefront sensing is used in adaptive optics techniques to compensate optical distortions for maximizing system performance.
A commonly used method for wavefront sensing is Shack-Hartmann sensors. Shack-Hartmann sensors make use of an array of lenses (lenslets) of the same focal length. Each lenslet is focused onto a photon sensor. A local tilt of a wavefront across each lens can then be calculated from a position of a focal spot on the sensor. By sampling an array of lenslets, all of these tilts can be measured and the whole wavefront approximated. However, a resolution of Shack-Hartmann sensors is limited by a size of a lenslet array pitch.
Another emerging method for wavefront sensing is to make use of interferometry. An interference pattern, or hologram, formed by an object beam, for which a wavefront measurement is to be performed, and a reference beam can be analyzed to create a digital reconstruction of the wavefront. However, a setup for creating the interference pattern is typically bulky, as a beam may first be split into the reference beam and the object beam, which is arranged to interact with an object to create a distorted wavefront allowing the object to be analyzed. Then the reference beam and the object beam, which has interacted with the object, may be combined to create the interference pattern.
In Palomo et al, “Characterization of the digital holographic wavefront sensor”, Proceedings of SPIE Vol. 9242: Remote Sensing of Clouds and the Atmosphere XIX; and Optics in Atmospheric Propagation and Adaptive Systems XVII, October 2014, a wavefront measurement which also makes use of holographic principles is disclosed. Here, a diffractive optical element is used, which contains holograms of one or several Zernike modes. The holographic sensor exhibits a linear response to an amplitude of a given Zernike mode present in the wavefront. Hence, by simply reading an intensity of light in certain positions of an image sensor, an aberration mode of the wavefront may be directly determined. However, this method may use a complex diffractive optical element.
Thus, it may be beneficial to improve methods and apparatuses for wavefront sensing in order to provide a less complex set-up.